The same is about an issue if it is possible to entrust your fiance to choose the ring by himself. I mean that there are couples where he and she have similar tastes and views, when they like the same things and all the time can find a compromise. But there is such a proverb that opposites attract. And for couples which fall within such a rule it is better to avoid surprises.
I can't even imagine how disappointing it is to get a ring you don't like. And despite the fact that my boyfriend and I have always the same opinions, if I were getting married, I would like to choose the rings together. The less the risk is, the better. Surprises are not so much appropriate when it comes to such serious stuff. Moreover, i don't see anything bad in choosing the ring together, since most girls have been dreaming about it since their childhood. Thus, this very part is responsible mission.